Bobby Jaggers did an interesting interview on wrestlingclassics in which he goes into the circumstances of Bruiser Brody's murder.
<a href='http://www.wrestling-videos.com/realaudio/1211rlmeta.ram' target='_blank'>http://www.wrestling-videos.com/realaudio/.../1211rlmeta.ram</a>

I think he broachs the subject somewhere around the 18th minute of the interview.

Yes, it was Invader 1 aka Jose Gonzales who stabbed Bruiser Brody while he was showering after one of their matches and Gonzales stabbed him and some Wrestlers where there, like Tony Atlas and some others.

Some Notes:
- Brody was indeed stabbed in the shower by Jose Gonzalez (known as Invader #1)
- Brody suffered a pierced lung in the stabbing
- Brody did indeed get an ambulance, albeit 40 minutes after the stabbing.
- Apparently, in Mantel's case, he recieved his subpoena after the trial was underway and in his words, "I had already heard the verdict by the time I opened the subpoena."